There are strong needs for a microchip in a clinical investigation and a proteomics analysis. The microchip is used to separate biomolecule such as nucleic acid and protein and to analyze the separated sample. In such an analysis of the sample, a method for optically detecting very small amounts of separated samples has been utilized. As a technique for optically analyzing the samples, a transmission light technique and a diffuse reflection technique are known.
According to the diffuse reflection technique, a sample is analyzed by detecting a reflected light of a laser light which is irradiated to the sample. A densitometry apparatus described in Japanese Laid-open Patent Application No. 2002-98637 employs a laser emitting device, and measures density of suspensoid composition contained in target liquid under measurement by using the diffuse reflection technique. In this densitometry apparatus, a plurality of optical fibers for generating the laser light and a plurality of optical fibers for receiving the laser light are bundled to configure a sensor unit.
On the other hand, FIG. 1 is a diagram showing a densitometry apparatus using the transmission light technique which is described in Japanese Laid-open Utility Model Application No. Sho-62-108858. In this densitometry apparatus, a light emitted from a light source 221 is led to a liquid channel 201 through a light leading optical fiber bundle 222, the light emitted from an end section of the light leading optical fiber bundle 222 is entered to an end section of a light receiving optical fiber bundle 223 through the liquid channel 201, and concentration of a liquid flowing in the liquid channel is measured by a photo detector 224.
Also, an optical type analyzer described in Japanese Laid-open Patent Application No. Hei-1-233345 is characterized in that a light emitted from a light source is branched into a plurality of channels by a branching optical fiber. A light in one branched channel is entered to a reference light receiving device without entering to a sample. Lights in the other branched channels are entered to the sample, and the lights passing through the sample are entered to a sample light receiving device.
FIG. 2 is a diagram for showing a capillary electrophoresis apparatus described in Japanese Laid-open Patent Application No. Hei-9-288090. This capillary electrophoresis apparatus consists of a substrate 114 on which a channel 120 is formed, an optical fiber 108 embedded in the substrate 114, a light source 103 connected to the optical fiber 108, and a photo detector 135 connected to the substrate 114. In the apparatus, the photo detector 135 is provided above the channel 120, and a sample liquid is conducted into the channel under such a condition that the sample liquid is made dielectric by using fluorescent reagent. A sample excitation light is conducted from the light source 103 to the other end of the optical fiber 108, and the light derived from the optical fiber 108 is irradiated to a sensing section of the channel 120. The liquid sample receiving the light irradiation at the sensing section generates a fluorescent light, and the generated fluorescent light is entered to the photo detector 135.
According to a configuration in which the optical fiber bundles are arranged on both ends of the liquid channel as in the above-described densitometry apparatus described in the Japanese Laid-open Utility Model Application No. Sho-62-108858, it is difficult to align the light leading optical fiber bundle 222 with respect to the light receiving optical fiber bundle 223 correctly. As a result, there is such a risk that the concentration of the sample flowing through the channel cannot be measured in high precision.
In the case of the configuration in which the photo detector 135 is provided above the channel 120 as in the capillary electrophoresis apparatus described in the Japanese Laid-open Patent Application No. Hei-9-288090, it is difficult to secure the optical length enough to measure the absorption when the channel 120 is shallow and the observation is performed from the upper direction. Also, the optical fiber 108 is fixed by adhesive material to a groove 122 formed on the substrate 114. As a result, a process of fixing the optical fiber by using the adhesive material is necessary in addition to the positioning of the optical fiber. Thus, a method of manufacturing it becomes complex.